Conventional disc and stem butterfly valve throttling assemblies are typically one-piece disc stem models, two-piece through-stem models, or three-piece disc and upper/lower stem models, all which possess certain disadvantages. To note, one-piece disc stem butterfly valve assemblies are limited to construction with one type of material which may not be ideal for all the different parts and functions of the device, and are difficult and expensive to manufacture and repair. These conventional one-piece models are not preferred in many industries, such as the trucking or vehicular industry. Two-piece models, while allowing for the stem and disc to be constructed of different materials, are often cumbersome to assemble, lower flow volume, and, like the one-piece models, also suffer from complicated and expensive repairs. The conventional three-piece design has all the advantages of the one-piece and two-piece models, but is still expensive to manufacture and repair or difficult to disassemble for repair depending upon the particular design. Some of these conventional designs may also require external openings on the valve body to aid in lower stem installation or retention, which results in an additional source for corrosion, entry points for contaminates, and increased difficulties for repair.
Thus, there is a need for functional multiple-piece disc and stem embodiments which allow the use of dissimilar materials for stem and disc components; enable the stem component to be made of a stronger and/or more economical material than the disc component; are rebuildable; and, also allow for easy disassembly for replacement of wear components.